The phase change heat transfer of a gold particle irradiated by ultra-fast laser was studied by the two-dimensional dual temperature model. The position of the solid-liquid interface was determined by coupledly using the interface energy balance equation and the interface tracking method in nucleation dynamics. In addition, the effects of particle size on the sintering process were studied. The results show that when the laser irradiates the gold particle vertically, the melting phenomenon occurs mainly in the poles of the particle. The bottom of the particle melts earlier than the top and the melting volume is smaller. The difference of the particle size mainly affects the light intensity distribution and the heat transfer size. In the laser irradiation stage, due to the scattering effect, the particle size becomes larger and the bottom light intensity becomes bigger, which raises the bottom temperature. When the laser irradiation has finished, the larger particle size leads to a larger heat-transfer volume, which leads to a decrease in the particle temperature and the melting rate.